This invention relates to a method of manufacturing siloxanyl phosphate, and specifically, it relates to a method for producing siloxanyl phosphate under moderate conditions at a fast rate, to produce a siloxanyl phosphate which is of high viscosity and of low phosphoric acid content and which can be used as a neutralization agent for the basic catalyst used in manufacturing processes for high viscosity diorganopolysiloxanes.
The ring-opening polymerization of cyclic diorganopolysiloxanes catalyzed by a basic catalyst, namely, alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, cesium hydroxide, lithium hydroxide, etc., or silanolates or siloxanates of these alkali metals, or the condensation polymerization of .alpha.,.omega.-hydroxyl-capped diorganopolysiloxane by the above basic catalyst, followed by the neutralization of the basic catalyst by acidic substances are well known methods for manufacturing high viscosity diorganopolysiloxanes. In general, the acidic substance used as the neutralization agent for the above basic catalyst can be specifically, hydrochloric acid, acetic acid, phosphoric acid, carbon dioxide, etc. However, the hydrochloric acid and acetic acid added have to be weighed out exactly to their theoretical quantity against the basic catalyst in the diorganopolysiloxane, because the heat resistance of the diorganopolysiloxane obtained is degraded by excess basic catalyst or by excess acidic substance. Also, when carbon dioxide, which is a weak acid, is used, the neutralization salt produced by the neutralization of the basic catalyst in the diorganopolysiloxane decomposes at elevated temperatures and forms a basic substance again. Therefore, this neutralization salt has to be removed completely from the diorganopolysiloxane, or otherwise the heat resistance of the diorganopolysiloxane obtained is generally poor.
Phosphoric acid is a preferable neutralization agent in that the phosphate produced by neutralization with the basic catalyst in the diorganopolysiloxane functions as a buffer for the residual phosphoric acid or basic catalyst even if its addition amount is not weighed out exactly to the theoretical quantity against the basic catalyst in the diorganopolysiloxane, and therefore suppresses the heat resistance degradation of the diorganopolysiloxane. However, phosphoric acid is, similarly to other acidic substances such as hydrochloric acid, acetic acid, etc., insoluble in diorganopolysiloxane, and therefore, its mixing and contacting efficiency during the neutralization process is low, and it has been a problem that its neutralization time is too long.
Because of this situation, phosphoric acid-containing organic silicon compounds such as silylphosphate, siloxanyl phosphate, etc. have been studied as the neutralization agent for the basic catalyst in diorganopolysiloxanes. In particular, siloxanyl phosphate is of merit since its viscosity is higher compared to silylphosphate. Therefore, the neutralization time can be shortened drastically by the improved miscibility with the diorganopolysiloxane when it is used as the neutralization agent of the basic catalyst in the manufacturing process of the high viscosity diorganopolysiloxane using the above basic catalyst. Also, siloxanyl phosphate is of merit since its phosphoric acid content in a molecule is less than that of silylphosphate, and even if it is not weighed out correctly to its theoretical quantity against the basic catalyst, this error in the theoretical quantity against the above basic catalyst can be smaller.
Manufacturing methods for siloxanyl phosphates which have such merits is illustrated, for example, by a method of manufacturing siloxanyl phosphate where phosphoric acid or a phosphorus halide compound and hexaorganodisiloxane and triorganosiloxy-capped diorganopolysiloxane are heated to react while removing generated water (refer to JP (Kokai) 54-89000). A method of manufacturing siloxanyl phosphate is taught where phosphoric acid and triorganosiloxy-capped diorganopolysiloxane are reacted in the presence of silylphosphate catalyst (refer to JP (Kokai) 54-109924). A method of manufacturing siloxanyl phosphate is taught where a silylphosphate mixture, which is prepared by adding phosphoric acid to hexaorganodisiloxane under heated reflux and heating while removing generated water, and cyclic diorganosiloxane are reacted (refer to JP (Kokai) 5-194557).
However, according to the manufacturing methods of siloxanyl phosphate proposed in the above patent journals, the reaction rate is slow without increased amount of phosphoric acid addition in the reaction system. Also, the reaction has to proceed at high temperatures in the range of 150.degree. C.-200.degree. C. for several hours since the reaction of siloxanyl phosphate is extremely slow under moderate conditions. Consequently, it has been a problem that the phosphoric acid content in the siloxanyl phosphate thus obtained is naturally greater. Furthermore, according to the manufacturing methods proposed in JP (Kokai) 54-109924 and JP (Kokai) 5-194557, the reaction does not proceed at all without silylphosphate. Therefore, it is necessary to prepare silylphosphate beforehand, and this creates a problem in that the manufacturing process for siloxanyl phosphate becomes complex.
The objective of the present invention is to provide a manufacturing method for a high viscosity and low phosphoric acid content siloxanyl phosphate, which can be used as neutralization agent for the basic catalyst used in a manufacturing process for high viscosity diorganopolysiloxanes and which can neutralize the basic catalyst quickly under moderate conditions.